I would guess they probably found that the "small business" segment of their customers ended up contributing to a disproportional percentage of fraud, support r

I would guess they probably found that the "small business" segment of their customers ended up contributing to a disproportional percentage of fraud, support requests, etc, to the point they were net negative? Though I still wonder if they considered just closing off to new customers instead of closing accounts of existing ones, since the fact that the latter would blow up in a nasty PR nightmare like this and do massive damage to their brand was pretty foreseeable.